| Bill,
That's one reason why I asked the question about the rotary being more like a 2-stroke when it comes to exhaust design. The other is that there is no exhaust valve to open and close. Instead, there is a revolving door that passes across the exhaust port, never really closing. So, I took Ed's recommendation and ordered the book on how to hot rod the rotary engine. There's a chapter on exhaust design that I'm hoping will explain all this in terms that I can understand.
Mark On Sat, Nov 20, 2010 at 8:42 PM, Bill Bradburry <bbradburry@bellsouth.net> wrote:
Here is where I show my lack of
understanding….
Isn’t 40 cu in the size of one rotor
and shouldn’t this calculation be based on the rotor faces instead of the
entire rotor? With a recip engine the exhaust valve on a
cylinder opens once every other revolution of the crankshaft, but with the
rotary, a rotor face exhausts every revolution of the e-shaft. So there
are twice as many pulses in a rotary header pipe as in a recip header.
So can the calc for a recip be used for a
rotary without some modifications?
Bill B
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Ed Anderson
Sent: Saturday, November 20, 2010
12:21 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Exhaust
Calcuations
I did some algebraic manipulations to find HPL based on a
selected HPD (tube diameter) and got an answer. However, I am
somewhat skeptical of it although it does tend to fit with the general theory
of larger dia pipes = shorter lengths.
By arbitrary selection an diameter - you
automatically select the rpm factor in the equation (but, its hidden
in the HPD value). The way you check what your new rpm sweet spot
with the arbitrary diameter is to vary the rpm in the first set of equations
until you get the length determined by manipulated equation.
So the revised equation for 1.8" dia tubes gave
27.58" inches for the HPL. You vary the rpm value in the first
equations until you get an HPL of 27.58" and you get an rpm of approx 7900
- so I agree, probably too high for your configuration.
Sent: Saturday,
November 20, 2010 11:18 AM
Subject:
[FlyRotary] Re: Exhaust Calcuations
Ed,
OK, that answers my question. By going with 1-7/8" OD pipe
(.049 wall), it would be tuned for about 7800 rpm. Obviously, this is too
high for our purposes. I'll go with 1-5/8 (.063 wall) to shoot for 6700
rpm peak power. This is typically the rpm I see on ground roll and early
climb before I start adjusting the prop down to a lower rpm to transition to
cruise climb.
Have you used the header designer tool available from Burns Stainless?
You need to know all the timing numbers, rpm, etc. I may give it a
try and see what I come up with. I have a test p-port housing that I made
up to see if the tube could be welded to the inner liner. So, I can use
that with a spare rotor to verify the EVO and EVC numbers.
|